1. Field of the Invention
The present invention relates to an improved internal construction of a variable capacity wobble plate type refrigerant compressor, and more particularly, to an improved structure for mounting, on a compressor drive shaft, a coil spring or springs which constantly apply a biasing force to a wobble plate, an inclination of which is changed with respect to a plane vertical to the axis of the drive shaft, to thus vary the stroke of pistons of the compressor and thereby change the compressor capacity
2. Description of the Related Art
Japanese Unexamined ( Kokai ) Patent publication No. 62 - 55478 published on Mar. 11, 1987 and Japanese Unexamined ( Kokai ) Utility Model publication No. 1 - 83185 automatically published on June 2, 1989, by the Japanese Patent Office, disclose a variable capacity wobble plate type refrigerant compressor provided with a rotatable drive shaft, a reciprocating piston type compressing mechanism to pump in a refrigerant before compression, compress the refrigerant, and discharge the refrigerant after compression, and an assembly of drive and wobble plates mounted around the drive shaft, an inclination of which can be changed with respect to a plane vertical to the axis of the drive shaft to change the stroke of the reciprocation of the pistons and thereby vary a discharge capacity of the compressor. The variable capacity wobble plate type refrigerant compressor is further provided with a coil spring mounted around the drive shaft, to constantly apply a biasing force to the assembly of the drive and wobble plates toward a small inclination angle position and thereby shift the assembly to a predetermined position corresponding to the smallest capacity position when the compressor is stopped. Due to the provision of the above-mentioned coil spring, when the variable capacity compressor is accommodated in a car air-conditioner, starting of the compressor driven by a car engine via a rotation transmission mechanism can be prevented under a condition such that the reciprocating piston type compressing mechanism exhibits the maximum reciprocation stroke thereof, and accordingly, a mechanical shock which usually occurs at the start of operation of the compressor can be limited to a smallest possible extent. Also, when the assembly of the drive and wobble plates is urged by the coil spring toward a small inclination angle position thereof, a compression of the liquid phase refrigerant does not occur even if the liquid phase refrigerant is pumped into the compressor from the external circuit of the air-conditioner at the moment of starting of the compressor, and therefore, damage to or a breaking of the internal components of the compressor due to the compressing of the liquid phase refrigerant does not occur.
U.S Pat. No. 4,934,157 to I. Takanashi et al which is assigned to the same assignee as for the present application, discloses a variable capacity wobble plate type compressor in which a pressure within a crankcase chamber for accommodating therein an assembly of drive and wobble plates is adjusted by controlling the duty ratio of a solenoid-operated pressure control valve, to adjustably change an angle of inclination of the drive and wobble plate assembly with respect to a plane vertical to the axis of a compressor drive shaft.
The compressor of U.S. Pat. No. 4,934,157 employs a spring element mounted around the compressor drive shaft for constantly urging the drive and wobble plate assembly from a small inclination angle position corresponding to a small discharge capacity position toward a larger inclination angle position corresponding to a large discharge capacity position, to thereby obtain a quick change of the drive and wobble plate assembly from the small discharge capacity position toward the large discharge capacity position.
FIG. 4 illustrates a further example of a conventional variable capacity refrigerant compressor corresponding to a compressor disclosed in Japanese Unexamined ( Kokai ) Patent publication No. 61 - 171886 published on Aug. 2, 1986, by the Japanese Patent Office. The compressor shown in FIG. 4 has a swash plate 42 arranged within a crankcase chamber 41 and tiltably supported on a ball-shaped slider 44, which is slidable on a drive shaft 43. The swash plate 42 is engaged, via a hinge mechanism 46, with a rotating element 45 rotatable with the drive shaft 43, and further engaged, via a pair of ball-shaped shoes 48, with each of a plurality of reciprocatory pistons 47. Therefore, the rotation of the swash plate 42 causes the reciprocation of the pistons 47 within a cylinder bore to compress a refrigerant gas in the cylinder bores. The compressor of FIG. 4 is provided with a coil spring 49 arranged between the slider 44 and the rotating element 45 to constantly urge the swash plate 42 toward a small discharge capacity position thereof.
Nevertheless, in the above-described conventional variable capacity refrigerant compressors, the spring element, particularly the coil spring, is usually coiled around the drive shaft of the compressor and is in contact with the cylindrical surface of the drive shaft, and accordingly, when the coil spring is frequently subjected to contraction and expansion in response to a change in an inclination angle of the drive and wobble plate assembly, the coil spring and the surface of the drive shaft are gradually abraded. Further, during the operation of the compressor with a constant inclination angle of the assembly of drive and swash plates, the coil spring is vibrated at an intermediate portion thereof by either sensing or resonating with a vibration due to the compressing and discharging motion of the compressor. Accordingly, the intermediate portion of the coil spring in contact with the surface of the drive shaft is gradually abraded during the vibration thereof, and the surface of the drive shaft of the compressor is also abraded. The abrasion of the coil spring causes a degradation of the elasticity and a shortening of the life of the coil spring, and consequently, the performance of the compressor per se is gradually degraded over a long term use thereof.